Instruction Manual
EMT 240
Reverb Foil
CONTACT: BIRDGETTE HEBDING nee (ZIMMER)
BARCO-EMT
GERMANY
TELEPHONE: 0114978259060
ATTENTION!
The unit contains an additional protection against shock, in order to
prevent any damages caused by shock or other impacts due to rough handling
in transit.
Before operation please remove the shock protection in the following sequence:
Open one side of the housing - take the wrench of the accessories and
loosen nuts at the lower wooden blocks until the bolts will release the
inside housing - take of f laterally the squeezed upper blocks - take off
laterally the lower blocks.
The inside housing should now swing freely in all directions.
If shipment has to be made by you occasionally via carriers, such
as railway, airfreight or forwarding agents, we would recommend in your
own interest to re-mount the shock protection and to ship the unit only in
its original packing.
The shock protection and the packing is not necessary for transportation
by car, truck or Broadcasting Van, provided the unit is handled with care
during such transportation and when loading and unloading the equipment.
8. July 1977 Vo/sh/ge
1
You have acquired a precision instrument when
you bought the EMT 240 Reverb Foil. It was designed for field use and is therefore made to
withstand mechanical shock found under normal
operating conditions. Do not subject the
Unpacking instructions and
preliminary set-up
You have just opened the outer packing case
— please read on before you unpack the unit any
further.
unit to excessive accellerations — treat it with the
same care with which you would handle a tape
recorder, for example. This will assure that the
excellent performance specifications of the EMT
240 will be maintained for some time to come.
1. Remove the foam cushions on top of and on
the left and right of the inner carton. Check to
see that all of the accessories in the plastic
covered boards correspond to the list on page
4.
2. Carefully lift out the inside carton. Do not lay
the unit on its side under any circumstances!
3. Open inside carton.
4. ATTENTION!
The unit contains an a d d it io n a I protection
against shock, in order to prevent any damages caused by shock or other impacts due to
rough handling in transit.
Before operation please remove the shock
protection in the following sequence:
Open one side of the housing — take the wrench
of the accessories and loosen nuts at the lower
wooden blocks until the bolts will release the
inside housing — take off laterally the squeezed
upper blocks — take off laterally the lower
blocks.
The inside housing should now swing freely in
all directions.
If shipment has to be made by you occasionally via carriers, such as railway, airfreight or
forwarding agents, we would recommend in
your own interest to re-mount the shock protection and to ship the unit only in its original
packing.
The shock protection and the packing is not
necessary for transportation by car, truck or
Broadcasting Van, provided the unit is handled
with care during such transportation and when
loading and unloading the equipment.
5. Locate unit at desired spot and connect electrically (page 8). Check proper line voltage setting!
Turn unit on. Push the reverberation time
button (—) for about 10 seconds. The unit is
now ready for operation.
6. Save all packing materials! Re-ship only in the
original packing.
TRANSPORT IN UPRIGHT POSITION
ONLY!
2
Technical Description
The Reverb Foil EMT 240 is a device for producing reverberation.
The principle involving the use of a flat, tensioned
plate for the creation of reverberation, which has
been used for the past decades, has been retained in this new device. In the course of technical improvement and the significant reduction in
size, the material used in the vibrating plate has
also been changed: The EMT 240 Reverb Foil
uses an electroplated gold foil of great purity (24
carat “coin gold”) with a thickness of only 18j.jm
(.00071”) and 270x290 mm (10.6”xl 1.4”) size.
This foil is mounted in a frame under tension,
excited by a driver, and sensed by a pick-up
system.
Changing the Reverberation Time
The reverberation time is changed as before by
bringing a damping device in close proximity to
the foil. A vibrating foil such as this gives off
energy to the surrounding air (sound field); by
bringing an absorber more or less close to this
sound field, energy is removed and the decay is
damped to a greater or lesser extent.
This method not only has the advantage of damping all frequencies equally and without erratic
behavior (as may occur due to the complex input
impedance of a mechanical system when damping is done electrically by changing the impedance of the transducer), but it is also possible,
using suitable means, to make this absorption
frequency dependent and thereby to compensate
the response of the reverberation time. These
frequency dependent resistances are produced
by openings in the damping plate. The picture
shows slots in the actual damping material which
serve this purpose. By varying the slot widths and
the ratio between slot and damping surface, the
required equalization is obtained.
Remote Reverberation Time Control
The damping plate may be moved by remote
control. A complete description, including connection means, is given on page 9.
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4
5
6
7
Alignment and Calibration
IMPORTANT! A reverberation time of 2 seconds is to be set for all measurements!
applicable from serial no.139 on
The level alignment of the Reverb Foil EMT 240 may be undertaken in various ways, all of which produce the
same result.
1. Alignment according to the “Braunbuch” specifications 054 or V 54, only applicable to studio systems
set up according to “IRT BRAUNBUCH” specifications:
Feed a test signal of 1 kHz at 0 dBabs from a low impedance source oscillator (Ri’ 50 ohm) to the input. 1.2.
Measure at the test jack using a high impedance volt meter or multi-meter (Ri’ 10 kohm/volt); set INPUT
potentiometer to produce reading of 0.245 V (^ -10 dBabs)
1.3. Replace the test signal with a 1 kHz third octave white noise signal (e.g. part 1 of the Reverberation test
tape) at a level of 0 dB. Adjust OUTPUT potentiometer so that 0 dB level is measured at the output of the unit.
Since the measuring instrument used influences the reading of white noise level, it is recommended that the
same meter be used both for measuring input and output levels.
2. Alignment for studio systems using peak level indicators and any peak alignment levels:
2.2.
2.1. Feed a test signal of 2 kHz at standard
line level (e.g. +6 dB) from a low
impedance source oscillator (
50 ohm) to the input.
Measure at the test jack using a voltmeter, peak level indicator or high
impedance multi meter ( 0 kohm/
volt); set the INPUT potentiometer to
produce a reading of 0.49 V
( -4 dB).
2.3. Replace the test signal with a 1 kHz third-octave white noise signal (e.g. part 1 of the reverberation test
tape) at standard line level (measured using studio peak indicator). Adjust OUTPUT potentiometer so that
standard line level also appears on the peak indicator at the output of the unit.
3. Alignment using vu meter:
3.1. Feed a test signal of 1 kHz at standard line level (e.g. +4, +6, or +8 dB) reading ZERO on your standard
vu meter with proper vu range pad, to the unit’s input.
3.2. Measure at the test jack using a high
impedance volt meter or multi-meter
( 210 kohm/volt); set the INPUT potentiometer to produce a reading of
0.245 V -10 dB abs 8
Replace the test signal with a 1 kHz thirdoctave white noise signal (e.g. part 1
of reverberation test tape) or
program material at standard line level
measured using your standard vu
meter) and adjust OUTPUT potentiometer so that identical levels appear
both at the input and output of each
channel.
To check the transmission characteristics and to facilitate alignment of the Reverb Foil EMT 240 we can supply
a test tape (tape speed 15 ips (38.1 cm/s) equalization IEC/CCIR) which obviates the use of white noise generator and third-octave filter. This test tape has the following program:
1. Level alignment part
Announcement; Third-octave band white noise; mid frequency 1 kHz; peak recording level; duration approximately 2 min.
Yellow leader
2. Frequency response part
Announcement; Third-octave band white noise. 27 mid frequencies from 40 Hz - 12.5 kHz each with announcement; (duration each band 20 s) 14 dB under peak recording level.
Alignment using sine wave signal is not possible since the reverb foil - as with every echo chamber - produces a
multitude of closely spaced self-resonances and therefore would yield a highly frequency dependent output
level.
The frequency response is also best determined using third-octave white noise, but otherwise measured as usual:
The output level as a function of frequency is measured with a constant level (-14 dB) at the reverberation unit
input. The response should lie within the tolerance (low frequency cut-off filter in O dB position).
In general it can be stated that minor deviations from the tolerances are not acoustically noticeable.
A level recorder permits this measurement to be made using a sweep signal. The time constant of the recorder
must be large enough so that the level variations for small shifts in frequency are integrated. Further information
regarding sweep frequency measurements may be found in the instructions for such equipment. The drive
section of the Amplifier EMT 262 may have its low frequencies attenuated with three different time constants.
The switch on the front panel of the amplifier is to be operated with a screw driver. The positions “0 dB” to “-24
dB” are shown in the response graph. Purpose of the low frequency cut-off: In a room the low frequency reverberation components always have a longer reverberation time than the high. Often it is desirable, from a production stand point, to reduce the low frequencies in the spectrum with respect to the high frequencies. In an echo
chamber this requires structural changes, such as low frequency absorbers. In the EMT Reverberation Foil, the
same effect is achieved with a multi-step, low frequency cut-off filter.
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Technical Data
Reverberation time
referred to 500 Hz
Noise level at Tr
= 2 5 Unweighted Signal-to-
Noise ratio, rms Weighted Signal-to-Noise
ratio, peak
Minimum input signal for full drive Peak mea-
sured vu measured
Input impedance
Maximum output level at 1 kHz and Tr
= 2 5
Usual reverberation
return level
Output source impedance
Minimum load resistance
Remote control
Control voltage requirement Power requirement
a) AC supply
b) DC supply
Weight
Dimensions
approx. 0.4 V rms
(— 5 dB)
~ 5 kQ balanced and floating
+ 21 dBm for 1% THD
—6...—l0dB, relative to direct channel
~ 40 Q balanced and floating
200 C)
Silicone damped linear motor with control elec-
tronics and position indicator.
24 VDC
I 0.25 A
switchable 200... 250 V or
100... l30V,50/60H~ 25VA
24 VDC I 0.8 A
67 kg (148 lbs.)
640x300X625 mm
(251A” x 12” x 25”)
(w x d x h)
Subject to change.
0,7...55
~ 65 dB ~ 60dB
0.775V rms (0 dB)
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15
16
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RL: EMT 240
Alignment hints for units beginning with serial No.
EMT
262
beginning with serial No. 23337).
195
(with Amplifier
Beginning with the above named serial numbers, the drive aznplificrs have
been coupled v~.a pin
5 of the amplifier connector.
The heretofore published level indications are still valid, but for calibration
or operation with one amplifier inserted.
There are three alignment possibilities:
Input: 0 dB, f= 1 kHz (third octave white noise)
and T = 2 sec, produces at the Output:
Test Jack Audio Output
I. 1 amplifier plugged into unit -10 dB 0 dB
II. 2 amplifiers plugged into unit,
feed to only one input -.16 dB ..3 dB
III. 2 amplifiers plugged into unit,
both irputs fed from same source -10 dB +3 dB
Note: Measure the level at the test jack using high impedance millivolt
meter, R1~1OO kQ.
Drive Amplifier:
For a 0 dB nominal line level, the level control R I (in tile amplifier,
ncctssible at the front panel) is to be adjueted so that a level of -13 dB
is obtained at test point (C).
The R128 potentiometer sets the limiter threshold. After nomiual alignment: input = output = 0 dB, application of a +8 dB signal to the input
~hould result in 0.5 dB limiting at the output.
The R 140 potentiometer determines the total amplificatio~i as ~ function
of the trcnsducer sensitivity.
4
The potentiometer R 140 (in the reverb unit, 22 k at the drive transformer) is to be adjusted to yield a level of -10 dB at the test jack.
Pickup amplifier:
The R 2 control (accessible at the front panel) determines tiie pick-up
amplification. For nominal amplification of approx, 81 dB, the weighted
noise level at the output should be -54 dB equivalent to an unweighted
noise of approx. <-62 dB peak
Note: The front panel accessible gain controls are set to the
foLLowin; scale marks for the standard factory alignment:
input : 5 - 7
output: approx. 7
Kippenheim, May 27th, 1975
P1/sh
18
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